The present invention relates to the field of power supply circuits, and more particularly to charge pumps and switching power stages employing charge pumps.
There are a variety of applications employing power stages utilizing high-voltage switching devices, typically field-effect transistors (FETs) in recent times. One or more FETs are coupled between a power source and a load, and control circuitry controls the switching action of each FET in a coordinated manner to achieve a desired operation. Examples include switching DC power supplies in electronic systems, DC motors such as used in aircraft actuators, and other applications. Such systems often include gate drive circuitry for each of the power FETs to provide proper bias and drive levels. Typically the gate drive circuitry for a FET includes smaller switching transistors that receive low-level control signals from the control circuitry and selectively apply relatively large voltages to the gate of the FET to effect the desired switching of load current. In many applications, the control signals provided to the gate drive circuitry are electrical signals generated directly by the control circuitry.
In some applications, it is desired to isolate the high-power electronics from the control circuitry, in which case the control signals may be in the form of optical signals conveyed by an optical fiber for example. Generally, isolation is maintained in order to protect the relatively sensitive control circuitry and signals therein from disruption that might be caused in a more noisy or otherwise hazardous environment in which the high-power circuitry operates. As an example, in military aerospace applications there is a move toward so-called “fly by light” systems in which the control signals that control the operation of heavy-duty actuators for flight surfaces (rudders, flaps etc.) are conveyed in optical form so that the control circuitry remains protected within the body of the aircraft, rather than being exposed to microwave or other electromagnetic interference that may be present outside the aircraft. In these kinds of applications it is necessary for the gate drive circuitry to be responsive to the optical control signal, such as by use of so-called light-sensitive switches (LSSs) or similar technology.
As noted, it is known to use high-power FETs as switching device for delivering power to an electrical load. For many years, there has been widespread use of enhancement-mode N-channel FETs made of doped silicon. More recently, other FET types are being used because of certain advantages they might enjoy over silicon FETs. Currently there is interest in the use of junction FETs (JFETs) based on silicon carbide (SiC) material. In particular, these devices exhibit relatively high immunity to electromagnetic interference (EMI) and high temperature operation, for example, and thus may be better suited for use in hostile EMI environments.
It is known to use circuits called “charge pumps” for a variety of applications. Charge pumps are often used to generate relatively high voltages from much smaller supply voltages, for example. Systems requiring such high operating voltages may include those including gas discharge lamps, semiconductor devices using super-voltages as programming voltages, etc.